Generally, my invention relates to a trocar which penetrates a body cavity for laprascopic procedures. More specifically, the present invention relates to a trocar with an improved profile which reduces the force necessary for insertion of the trocar into a body cavity. The improved trocar of this invention allows the user of the trocar to perform the insertion procedure with greater safety than through the use of devices known in the prior art.
Trocars are devices used in conjunction with minimal invasive surgery. The trocar is a combination of a blade and a cannula. The device is constructed so that once it penetrates the various body layers and enters a body cavity, the blade can be withdrawn leaving a cannula functioning as a channel for the insertion of surgical instruments into the body cavity for use in performing the surgical procedure.
In its specific application, this invention relates to and is used in connection with a laprascopic procedure such as laprascopic cholecystectomy. Such a procedure usually begins by the surgeon inserting a hollow needle into the abdominal cavity to introduce a gas under pressure to insufflate the cavity for creation of a work space for the procedure. A self sealing trocar, consisting of an outer cannula and an inner penetrating mandrel or blade extended beyond the distal end of the assembly, is then used to penetrate the abdominal wall. The outer cannula is forced, along with the blade, through the various layers forming the outer wall of the body and finally through the peritoneum and into the abdominal cavity. After the penetration process is completed, the blade is withdrawn, creating a channel along the length of the cannula through which various instruments are inserted for performing the laprascopic procedure.
A problem that occurs occasionally during the trocar insertion procedure is the inadvertent puncturing of organs inside the cavity with the trocar blade. If an organ is inadvertently punctured during the procedure, what began as minimal invasive surgery may become a major operation and may require open cavity surgery to repair the punctured organ.
It has been determined that one of the reasons that the procedure occasionally results in a punctured organ is because of the magnitude and inconsistency of the force required to penetrate the abdominal wall. Studies have shown [See, e.g., Corson, et al, Journal of Reproductive Medicine pp. 282-84 (1989)] that the insertion force required for both disposable and reusable trocars varies from 3.0 to 34 lbs.
When the trocar is being inserted through the abdominal wall, the physician is applying pressure against the proximal end of the trocar and the dominant counteracting force to the force created by the pressure of the physician is the force exerted by the insufflation gas on the abdominal wall. For typical insufflation pressures of 15 mm of Hg., the total force exerted on the wall is less than 15 lbs. for a typical 50 sq. in. abdominal size. Insertion forces substantially greater than 15 lbs. will compress the abdomen substantially toward vital organs. Often the surgeon meets high resistive forces due to the strong fascia layers which halt smooth entry of the trocar. Final penetration often occurs in a quick catastrophic fashion such that the physician is unable to react to avoid puncturing vital organs.
The fascia layer is a sinewy web-like structure of substantial strength. With trocars of the type that have been used in the past, particularly those in which there is a step created on the outer surface of the trocar by the engagement of the cannula about the outer perimeter blade extending from the distal end of the cannula, the step of such prior structures tends to bind against the fascia layer and cause greater resistance to penetration. When enough pressure is applied to the proximal end of the trocar, it will eventually force the stepped shoulder of the prior art cannula through the fascia and when that occurs, the resisting force against the force being applied by the physician is quickly released so that the trocar proceeds rapidly through the abdominal wall.
The prior art has primarily been directed at attempts to react to the problem rather than to eliminate the problem. The efforts of the prior art include so-called "safety shields" which are designed to cover the blade as soon as the peritoneum has been penetrated. U.S. Pat. Nos. 4,535,773 and 4,601,710 disclose such shields that enclose the blade. These shields are equipped with a spring loaded bias. The act of pushing the distal end of the trocar assembly against the abdominal wall moves the shield against the bias in the proximal direction, thereby exposing the blade. When the friction force between the abdominal wall layers and the safety shield exceed the bias force, the trocar enters the body cavity, the friction forces are released and the spring bias force causes the shield to move distally to again cover the blade. The problem with the prior art is two-fold. First, the blade breaks through the peritoneum significantly prior to the shield and, therefore the blade must be inside the cavity by a substantial length before the shield activates. Second, and compounding the problem, is the fact that the shield diameter is larger than the blade, thereby increasing the frictional forces from surrounding tissue as the trocar is forced through the abdominal wall. Because of the great force that must be exerted against the trocar to cause it to penetrate the abdominal wall, and since that force is increased by the increased diameter of the shield surrounding the blade, once actual penetration into the abdominal cavity is achieved, the resisting force is released and the tendency is for the trocar to accelerate rapidly into the body cavity and puncture vital organs.
In the use of prior art devices, including those devices carrying safety shields, the insertion forces necessary to cause penetration are often substantially greater than the 15 lbs. of force created by the insufflation process. Thus, the abdomen is compressed substantially toward vital organs so that the shield may not have time or room to activate. The bias force on the socalled "safety shield" must be overcome before the blade is exposed and thus adds to the overall insertion force requirement. Also, the force required to penetrate the cavity increases the pressure of the insufflating gas inside the cavity by decreasing the volume of the cavity and thereby increasing the risk of embolism.
What is needed then is a safety trocar which will substantially reduce the force required for insertion of the trocar.
It is therefore an object to the present invention to provide a safety trocar which does in fact reduce the insertion force requirement.
It is a further object of the present invention to provide a safety trocar that reduces the insertion force requirements yet is simple and easy to manufacture at a minimum cost as compared to prior art devices.
It is still another object of the present invention to provide a safety trocar which has a unique profile that reduces the insertion force requirements when the trocar is used to penetrate the abdominal wall.
It is still another object of the present invention to provide a safety trocar that requires a consistent and low insertion force, preferably in the 2 to 4 lb. range.
These and other objects of the invention will be more clearly understood when the detailed description of the preferred embodiment is considered in conjunction with the drawings made a part of this application.